1. Field of the Invention
The present invention relates to a thin-film magnetic head comprising a magneto-resistive effect device for reading the magnetic field strength of a magnetic recording medium or the like as signals, and a head gimbal assembly and a magnetic disk system, each comprising that thin-film magnetic head.
2. Explanation of the Prior Art
In recent years, with an increase in the plane recording density of magnetic disk systems, there have been growing demands for improvements in the performance of thin-film magnetic heads. For the thin-film magnetic head, a composite type thin-film magnetic head has been widely used, which has a structure wherein a reproducing head having a read-only magneto-resistive effect device (hereinafter often called the MR device) and a recording head having a write-only induction type magnetic device are stacked together.
The MR device, for instance, includes an AMR device harnessing the anisotropic magneto-resistive effect, a GMR device making use of the giant magneto-resistive effect, and a TMR device taking advantage of the tunnel-type magneto-resistive effect.
Requirements for reproducing heads, among others, are high sensitivity and high output. For reproducing heads meeting such requirements, GMR heads using a spin valve type GMR device have already been mass produced. The reproducing heads using a TMR device, too, are being mass produced so as to meet further improvements in the plane recording densities.
In general, the spin valve type GMR device comprises a nonmagnetic layer, a free layer formed on one surface of that nonmagnetic layer, a fixed magnetization layer formed on another surface of the nonmagnetic layer, and a pinning layer (generally an antiferromagnetic layer) on the side of the fixed magnetization layer facing away from the non-magnetic layer. The free layer has its magnetization direction changing depending on an external signal magnetic field, and the fixed magnetization layer has its magnetization direction fixed by a magnetic field from the pinning layer (antiferromagnetic layer). On each side of the device, there is a bias magnetic field-applying layer formed to apply a bias magnetic field to the free layer, thereby reducing Barkhausen noise.
By the way, common GMR heads used so far in the art have a CIP (current in plane) structure wherein a current for detecting magnetic signals (the so-called sense current) is passed parallel with the plane of each of the layers forming the GMR device (CIP-GMR device). On the other hand, GMR devices having the so-called CPP (current perpendicular to plane) structure wherein the sense current is passed perpendicularly to the plane of each of the layers forming the GMR device (CPP-MR device), too, are now under development as next-generation MR devices. The aforesaid TMR devices, too, would come under the CPP structure category according to a classification system from the current-passing direction alone.
A thin-film magnetic had comprising a magneto-resistive effect device of such CPP structure is in itself free of short circuits (poor insulation) between the device and the so-called magnetic shields located above and below that device. For this reason, the CPP structure could work much in favor of high recording densities.
As the recording density grows high, however, there are the following problems with the CPP structure: (1) as the device size becomes small and narrow, the head resistance grows high with degradation of the frequency characteristics, making it difficult for the device to adapt well to higher frequencies, (2) as the device size becomes small and narrow, it causes the volume of the device itself to decrease, and spins are likely to get erratic, resulting in an increase in the thermal magnetic noise and a worsening of the S/N ratio, (3) as the device size becomes small and narrow, the number of particles constituting the pinning layer (anti-ferromagnetic layer) or the bias magnetic field-applying layers declines, responsible for performance fluctuations, and so on.
In view of such situations, the invention has been made with a view to providing a thin-film magnetic head wherein even when device size becomes small and narrow, degradation of frequency characteristics is held back, any increase in the thermal magnetic noise is stayed off, and performance fluctuations are minimized.